There has been typically known a stratified scavenging two-stroke engine in which leading air is fed into a scavenging passage through a scavenging port (i.e., an opening of the scavenging passage that is opened in a combustion chamber), and the leading air is initially supplied to the combustion chamber through the scavenging passage prior to air-fuel mixture for scavenging, thereby suppressing blow-by of the air-fuel mixture.
In such a stratified scavenging stroke engine, there has been suggested that the scavenging passage include a main passage defined near an exhaust port and a sub passage defined near an intake port and a throttle as a flow rate adjuster be provided in the middle of the sub passage to reduce the inflow energy of the air-fuel mixture entering the combustion chamber, thereby suppressing the blow-by of the air-fuel mixture during the scavenging process (Patent Literature 1).